In recent years, a plating current has increased as a plating rate has increased in the electroplating field. A high plating current density of 30 to 250 A/dm.sup.2 is used for galvanizing or tinning a steel plate or manufacturing a metallic foil by the electroplating method. Moreover, it is requested to plate a banded material having a large width of 500 to 2,000 mm or obtain a metallic foil through electroplating. Therefore, to plate the large material, it is unavoidable that an insoluble electrode to be used increases in size. Moreover, in the case of manufacturing plated products or metallic foils, it is requested to further improve the quality of these products and keep the fluctuation of the inter-electrode distance between an anode and a cathode at 5% or less.
Therefore, it is attempted to use a composite electrode substrate obtained by using a conductive material such as copper, iron, aluminum, lead, or tin as a core and covering the core with a titanium plate for a large insoluble electrode to be operated at the above large current from the viewpoints of conductivity and profitability.
However, the above large composite electrode substrate has a considerably large weight and it is difficult to handle it when machining it. Moreover, the following problems occur when covering an electrode catalyst.
(a) A large heavy electrode substrate has a large heat capacity. Particularly, in the case of an insoluble anode manufactured by repeating heat treatment at a high temperature of 350 to 700.degree. C. and thereby covering an electrode catalyst such as a platinum-group metal or its oxide, the energy loss under heat treatment increases and moreover, it takes a lot of time to raise or lower the temperature.
(b) In the case of a composite electrode substrate, when covering an electrode catalyst, a joint between different types of metals is easily distorted or damaged.
(c) To cover an electrode catalyst, precision machining of the several-micron order is requested. Therefore, a considerably-high equipment cost is required to machine a large electrode substrate.
The official gazette of Japanese Utility Model Publication No. Hei 3-42043 discloses a device for solving the above problem. According to the device, it is possible to set or remove a second electrode substrate by using a composite electrode substrate as a first electrode substrate and supporting the second electrode made of a titanium plate covered with an electrode catalyst manufactured separately from the first electrode substrate to the first electrode substrate with a bolt.
Moreover, the official gazette of Japanese Patent Publication No. Hei 6-47758 discloses an art for deflecting a removable anode tie plate (second electrode substrate) by supporting the anode tie plate with a circular-arc electrolytic cell (first electrode substrate) having support means for supporting the anode tie plate in a circular-arc insoluble anode.
However, when an electrode becomes circular-arc, it is difficult to finish the first electrode substrate into a high-accuracy circular arc by the arts disclosed in the official gazettes of Japanese Utility Model Publication No. Hei 3-42043 and Japanese Patent Publication No. Hei 6-47758, differently from the case in which the first electrode substrate uses a plate. Therefore, it is difficult to decrease the fluctuation of the inter-electrode distance between an anode and a cathode even if supporting the second electrode substrate with the first electrode substrate. Moreover, a circular-arc electrode has a problem that fluctuation occurs in inter-electrode distances due to a slight deviation from the rotation axis of a cathode drum to be rotated.
To solve the problems, the official gazette of Japanese Patent Publication No. Hei 6-47758 further discloses an adjustment mechanism for keeping the gap between a cathode and an insoluble electrode constant. However, there are the following problems because adjustment is performed from the outside of an electrolytic cell (first electrode substrate).
Firstly, it is necessary to prevent support means for supporting an anode tie plate (second electrode substrate) with an electrolytic cell (first electrode substrate) from being wetted by liquid. Moreover, to use a mechanism for adjusting an anode tie plate (second electrode substrate), the structure becomes more complex.
Secondly, in the case of supporting an insoluble electrode to an electrolytic cell (first electrode substrate) by deflecting the electrode, a stress is applied to the covered layer of an electrode catalyst due to deflection. Therefore, when the electrode catalyst layer is used in a high-current-density region, it is deteriorated.
Thirdly, in the case of adjusting an insoluble electrode surface facing a cathode separately from the rotation axis of a cathode drum, it is necessary to adjust the position of the insoluble electrode surface at both the composite electrode substrate side and the insoluble electrode side. Therefore, the adjustment requires much time, or fine adjustment is difficult.
Fourthly, because adjustment is performed from the outside of an electrolytic cell (first electrode substrate), a large space is necessary.